1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus and an ultrasound diagnostic method, and more particularly to an ultrasound diagnostic apparatus and an ultrasound diagnostic method for taking an ultrasound image of a subject using ultrasound and displaying the ultrasound image.
2. Description of the Related Art
Conventionally, attempts have been made to measure a sound speed value in a part (a region to be diagnosed) in a subject (hereinafter referred to as a local sound speed value) using ultrasound. For example, proposed methods include a method of arranging two transducers for transmitting and receiving to face each other and obtaining a sound speed value in a subject based on a distance between the transducers and a propagation time of ultrasound, and a method of using two pairs of transducers arranged at a predetermined interval as the transducers for transmitting and receiving respectively and obtaining a propagation speed based on a propagation time of ultrasound between the transducers, wave transmitting angles and wave receiving angles, and the interval between the transducers of each pair.
Japanese Patent Application Laid-Open No. 5-95946 discloses a measurement method of a local sound speed value described below. In Japanese Patent Application Laid-Open No. 5-95946, a wave transmitting transducer transmits ultrasound into a subject while changing an emission angle, a wave receiving transducer receives the ultrasound while changing an incident angle, and times elapsing between transmitting and receiving of the ultrasound are all stored in a memory. Then, assumed sound speed distribution is set, and a time elapsing between transmitting and receiving of the ultrasound for each emission angle and each incident angle is calculated on the basis of the sound speed distribution. Then, the assumed sound speed distribution is corrected so as to minimize a difference between a calculated value and an actual measured value of the time, and a sound speed value in the subject is obtained from sound speed distribution obtained finally.